So I just started up minecraft with the new snapshot, and walked about until I found a jungle biome. I started to make a mine all the way to bedrock, but when I reached the bottom, I had a strange sound appear. It's sort of like a plunger sound that pops off, but it's very random and only occurs at the bottom of the mineshaft. I am in a jungle biome, so I don't know if it's an ocelot, but I can't measure that because ocelots only run about on grass which makes it impossible to hear their natural footstep.
I'm 100% sure it's a mob, I've tried both my headset and my speakers and it shows up on both, as well as the sounds being random. Tried digging around to no avail.